Long-term effects of wheat continuous cropping vs wheat in crop rotation on carbon content and mineralisation, aggregate stability, biological activity, and crop yield

Background: Crop rotation is an agronomic practice that can offer benefits such as increased soil aggregation, carbon storage, crop yield, nutrient transformation, and utilisation efficiency, alongside an increased abundance of microorganisms. As winter wheat is sensitive to certain forecrops, selecting suitable ones may influence productivity. Methods: This study assessed the impact of three forecrops on selected soil properties (carbon content, mineralisation, aggregate stability, and microbial biomass) at two soil depths and on wheat yield over three years. This approach introduced a novel evaluation of the interrelations between soil and crop traits. The experiment comprised the following variants: I. wheat after alfalfa (AW), II. wheat after maize (MW), and III. wheat in monoculture (WW). Results: Compared to wheat following alfalfa, wheat monoculture displayed higher total carbon and total organic carbon and the lowest relative residual oxidisable carbon (among all variants) at depth 2 (0.15-0.30 m). In variants where wheat followed different forecrops, significantly higher carbon mineralisation activities were observed at depth 2. The greatest increases in dehydrogenase, basal, and L-alanine-induced respiration (IR) were in the depth 2 of the MW variant, whereas in depth 1 (0-0.15 m) in the AW variant, the highest L-arginine-IR and fungal biomass were recorded. The WW showed increased soil aggregate stability between depth 1 and depth 2. The MW variant did not exhibit a significant depth-dependent effect on most properties. High bacterial biomass was associated with carbon mineralisation and with an increased proportion of recalcitrant carbon in both forecrops (AW, MW). These variants improved crop yield, number of spikes, and thousand-grain weight compared to WW. Conclusion: While forecrop practices were only moderately effective in enhancing soil carbon storage and stabilisation at soil depth 2, they contributed positively to soil microbial abundance, mineralisation activity, and grain yield.